New Catalyst to Support Acetic Acid Production from CO-sourced Captured Carbon

 Northwestern University researchers work with an international team of collaborators to create acetic acid out of carbon monoxide derived from captured carbon. The innovation, which uses a novel catalyst created in the lab of Professor Ted Sargent, could spur new interest in carbon capture and storage.

The need to capture CO2 and transport it for permanent storage or conversion into valued end uses is a national priority recently identified in the Bipartisan Infrastructure Law to move toward net-zero greenhouse gas emissions by 2050.

“Carbon capture is feasible today from a technical point of view, but not yet from an economic point of view,” Sargent said. “By using electrochemistry to convert captured carbon into products with established markets, we provide new pathways to improving these economics, as well as a more sustainable source for the industrial chemicals that we still need.”

“Acetic acid in vinegar needs to come from biological sources via fermentation because it’s consumed by humans,” Wicks said. “But about 90% of the acetic acid market is for feedstock in the manufacture of paints, coatings, adhesives and other products. Production at this scale is primarily derived from methanol, which comes from fossil fuels.”

Lifecycle assessment databases showed the team that for every kilogram of acetic acid produced from methanol, the process releases 1.6 kg of CO2.

Selectivity of Catalyst as Major Challenge:

Their alternative method takes place via a two-step process: first, captured gaseous CO2 is passed through an electrolyzer, where it reacts with water and electrons to form carbon monoxide (CO). Gaseous CO is then passed through a second electrolyzer, where another catalyst transforms it into various molecules containing two or more carbon atoms.

“A major challenge that we face is selectivity,” Wicks said. “Most of the catalysts used for this second step facilitate multiple simultaneous reactions, which leads to a mix of different two-carbon products that can be hard to separate and purify. What we tried to do here was set up conditions that favor one product above all others.”

In the paper, the team reports a faradic efficiency of 91%, meaning that 91 out of every 100 electrons pumped into the electrolyzers end up in the desired product, in this case, acetic acid.

“That’s the highest faradic efficiency for any multi-carbon product at a scalable current density we’ve seen reported,” Wicks said. “For example, catalysts targeting ethylene typically max out around 70% to 80%, so we’re significantly higher than that.”

The new catalyst also appears to be relatively stable: while the faradic efficiency of some catalysts tends to degrade over time, the team showed that it remained at a high level of 85% even after 820 hours of operation.

Source: Northwestern University/www.polymer-additives.speicialchem.com

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